This invention relates generally to a track laying vehicle and to apparatus and devices suitable for use in such a vehicle.
The track laying vehicle may be of the type comprising a main body having a longitudinal axis extending between its forward and rearward ends, a pair of track assemblies each disposed on opposite sides of the main body with each assembly comprising first and second wheels which are spaced apart in the direction of the longitudinal axis with at least one of the wheels defining a drive wheel.
There have been many attempts over the years to combine the advantages of tracks with the mobility and speed of pneumatic tires. A work vehicle using tracks converts more efficiently the engine power to pulling power than tires when worked on soft and/or loose surfaces. There is also less slippage and less compaction when comparing a tracked work vehicle and a rubber tired vehicle with the same weight to power ratio working on the same surface.
For many years, steel tracks have been the accepted form of tracks for a pulling and/or work vehicle, because they utilize a positive and mechanical drive between the drive wheel and the ground engaging track. However, steel tracks are generally limited to much lower maximum speeds because of their weight and wear characteristics. Steel tracks also have a relatively high noise level, higher initial cost and cannot be used on improved road surfaces without causing unacceptable damage. The high cost of repair to the joints of the steel track make them unacceptable for high speed applications. There have been many attempts to successfully use an elastomeric or rubber belt entrained around a driven wheel and an idler wheel to enable a tracked vehicle to work at higher speeds and retain the traction and flotation of steel tracks.
Previous inventions generally fall into two categories, positively driven belts and frictionally driven belts.
Many previous designs of positively driven elastomeric or rubber tracks have used two continuous belts joined laterally by inflexible ground engaging cross bars to provide a "chain and sprocket" type drive and to give lateral stiffness to the rubber track.
Still other positive drive tracks have used rubber belts with multiple rows of segments running longitudinally and protruding inwardly on the belt with opposite segments of each row being joined by an inflexible cross member to provide positive drive, and lateral engagement to the driving wheel and idler.
While many of these positive drive tracks achieve a certain amount of success, they are costly and complicated to manufacture, and have low levels of tolerance to debris ingestion and would tend to "clog up" when used in many farming applications.
Other attempts to use elastomeric or rubber tracks have been made by way of a frictional drive between the drive wheel and the belt by tensioning the idler wheel away from the drive wheel. Many of the friction drive systems have a dual purpose driving/guiding structure in the form of a "V" and running longitudinally on the inside of the belt to provide a guiding and driving means similar to a V-belt drive. The driving and guide grooves of the drive wheels, for this type of frictional drive, tend to accumulate a high level of debris and lose frictional drive through a lack of engagement on the side surfaces.
A more recent patent has been a frictional drive using flat lateral driving surfaces of the drive wheel and belt with a "dual wheel" drive and tensioning idler to accommodate guiding lugs extending inwardly on the belt which limits lateral movement between the wheels and the belt. This system relies heavily on a highly tensioned belt, which is at least eight hundred and fifty Newtons per lateral centimeter of belt, to maintain frictional drive.
There are a number of disadvantages with this type of frictional drive.
Firstly there is a significant level of parasitic power loss caused by the highly tensioned belt.
Breaking force and reverse thrust of the vehicle by means of the drive wheel is limited to, and directly related to the tensioning force of the idler wheel. Any braking force by means of the drive wheel higher than the tensioning force will cause the belt to "free wheel" around the outer surface of the drive wheel, creating a possible dangerous situation for the operator.
Frictional engagement between the drive wheel and the belt can be lost through the ingestion of a lubricating medium such as water, mud, and/or other friction reducing material. Any amount of this material will cause relative movement or slip between the drive wheel and the inner surface of the belt until a sufficient part of the inner belt's surface and the outer drive wheel surface have been cleaned or "wiped" to re-establish frictional contact. A continued ingestion of friction reducing material such as water and/or mud will cause continued slippage between the belt and the drive wheel resulting in lost drive and excessive wear of the contact surfaces.
While this type of frictionally driven work vehicle is commercially available it is generally limited to dry conditions to sustain maximum pull and intermittent ingestion of friction reducing material.